I have an interface like this

 public interface EventBus{
     public void fireEvent(GwtEvent<?> event);
 }

and test code(testng method) looks like this:

    @Test
    public void testFireEvent(){

          EventBus mock=mock(EventBus.class);

          //when  both Event1 and Event2 are subclasses of GwtEvent<?>
          mock.fireEvent(new Event1());
          mock.fireEvent(new Event2());

          //then
         verify(mock).fireEvent(argThat(new Event2Matcher()));

    }

Event2Matcher looks like this:

private class Event2Matcher extends ArgumentMatcher<Event2>
{
  @Override
  public boolean matches(Object arg)
  {
       return ((Event2) arg).getSth==sth;
  }
}

But get an error indicating that:

    Event1 can't be cast to Event2

And obviously,the matcher matched the first invoking

    mock.fireEvent(new Event1());

So,the statement within matcher

return ((Event2) arg).getSth==sth;

Will throw out this exception.So the question is how to let

  verify(mock).fireEvent(argThat(new Event2Matcher()));

to match the second invoking?